Two meanings:
1) A gay man who shaves his head bald and wears a goatee, in the attempt to appear more masculine. This man often speaks or acts feminine, but uses his new look to compensate for his femininity. Usually hangs out at straight bars for the rush of associating with heterosexual men, and in the gay scene, goes to so-called "leather and levi" bars for guys who like company of older men, SM practitioners, and fellow manpunks. The typical gay manpunk is between the ages of 30-45.

2) A man, straight or gay, over the age of 25, who acts and dresses like a punk, rocker, or other alternative music or social type in order to appear younger and socialize with younger people. Often wears concert tees for bands he doesn't listen to, wears Doc Martens on the weekends, and slavishly follows fashion trends in hairstyles, tattoos, and ear ornamentation.
Usually listens to pop punk bands and pop radio and assumes that this is hardcore rock or punk music.

My gay friend is a queen who likes to get plowed up the ass by manpunks.